Light recapture projection system

ABSTRACT

A projection system is disclosed comprising a light source, a first reflector proximate the light source, a second reflector proximate the light source, a light pipe, a color sequencing device a spatial light modulator and a target. The color sequencing device preferably directs three or more colors onto the spatial light modulator at a time. Some light is reflected from the color sequencing device back through the light pipe and is again reflected at the reflector at the light source before returning to the light pipe and color sequencing device. The brightness of the projection system is thereby increased.

[0001] This application claims priority to U.S. provisional application60/383,153 to Huibers filed May 23, 2002, the subject matter of which isincorporated herein by reference.

[0002] The present invention is in the field projection systems, and inparticular in the field of projection systems with sequential colorillumination of a spatial light modulator—that forms a color image on atarget. More particularly, the present invention is directed toincreasing light throughput in such sequential color projection systems,and in particular utilizing scrolling color and light recapture viarecycling through the light source.

SUMMARY OF THE INVENTION

[0003] In accordance with one embodiment of the invention a projectionsystem is disclosed, comprising: a point source of light and a reflectorproximate to the point source of light; a color sequencer, wherein thepoint source of light, reflector and color sequencer are arranged suchthat the light from the point source of light is directed so as to beincident on the color sequencer, and wherein at least 10% of the lightthat is reflected back from the color sequencer impinges on thereflector proximate to the point source of light and is reflected backso as to again be incident on the color sequencer.

[0004] In accordance with another aspect of the invention, a projectionsystem is disclosed, comprising: an arc lamp; a spherical reflectorproximate to the arc lamp; a color sequencer; wherein the arc lamp,spherical reflector and color sequencer are arranged in the projectionsystem such that the light from the arc lamp is directed so as to beincident on the color sequencer, and wherein at least a portion of lightthat is reflected back from the color sequencer impinges on thespherical reflector so as to reflected and again be incident on thecolor sequencer.

[0005] In accordance with a further aspect of the invention, aprojection system is disclosed, comprising: a UHP lamp having a dichroiccoating; a color sequencer; wherein the UHP lamp with dichroic coatingand color sequencer are arranged in the projection system such that thelight from the UHP lamp is directed so as to be incident on the colorsequencer, and wherein at least a portion of light that is reflectedback from the color sequencer impinges on the dichroic coating so as toreflected and again be incident on the color sequencer.

[0006] In accordance with a still further aspect of the invention, alight collecting system is disclosed comprising a color filter element;and a concentrated light source illuminating a color filter element;wherein a substantial portion of light that does not pass through saidcolor filter element is reflected back to said light source, andsubsequently is reflected back to said color filter element and thenpasses through a different location of said color filter element.

[0007] In accordance with yet another aspect of the invention, anoptical system is disclosed comprising: a multi spectral light source; areflector at the light source for reflecting light from the lightsource; a color sequencing device disposed to receive light from thereflector and that spatially passes some colors and reflects others backto the reflector, wherein at least 60% of the light that is reflectedfrom the color sequencing device is directed back onto the reflector atthe light source.

[0008] In accordance with yet another aspect of the invention, aprojection system is disclosed comprising: a light source and areflector proximate to the light source; a spatial light modulator; acolor sequencer that provides three or more different colors onto thespatial light modulator at the same time; wherein the light source,reflector and color sequencer are arranged such that the light from thelight source is directed so as to be incident on the color sequencer andhas a first etendue, and wherein light reflected back from the colorsequencer is incident on the reflector proximate to the light source andis reflected back so as to again be incident on the color sequencer witha second etendue less than 20% different from the first etendue.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an illustration of a projection system in accordancewith one embodiment of the invention;

[0010]FIG. 2 is an illustration of a projection system in accordancewith a second embodiment of the invention;

[0011]FIG. 3 is an illustration of a projection system in accordancewith a third embodiment of the invention;

[0012]FIG. 4 is an illustration of a projection system in accordancewith a fourth embodiment of the invention;

[0013]FIG. 5 is another embodiment of the invention where a sphericalreflector is used; and

[0014]FIG. 6 is an illustration of the light pipe superimposed on thecolor wheel.

DETAILED DESCRIPTION

[0015] The invention is described herein in relation to specificembodiments. Nevertheless, persons familiar with the field willappreciate that many variations exist in light of the embodimentsdescribed herein.

[0016] Sequential color systems (either full frame, partial frame, lineor pixel based systems) are useful because the same physical pixels canbe used to achieve all colors. By using an array of such pixels with acolor sequencer that sequences light into colors, it is possible to usea single pixel array and achieve a color image on a target. In thesesystems a detector (e.g. the human eye) serves to integrate thesequential light coming zfrom the display pixel elements, provided thatthe colors are shown in sequence faster than the response time of thedetector. Thus, a sequence of red, green and blue light onto a pixelarray (or a sequence of a spatial combination of red, green and bluelight), when sufficiently fast, will result in a full color image. Sucha projected image may be a still image (office or conferencepresentation) or a moving image (home theater).

[0017] In some sequential systems, a color wheel having red, green andblue segments is rotated through a white light beam resulting inconsecutive red, green and blue images on a light valve. The light valvecan be, for example, a liquid crystal light valve (transmissive orreflective) or a MEMS (micro electromechanical systems) type light valve(diffraction grating or micromirror array). In some sequential colorsystems, such as the Philips rotating prism based color system (JeffreyShimizu, Information Display, “Philips Scrolling-Color LCoS Engine forHDTV Rear Projection”, November 2001, pp. 14-19), the three colors areseparated and then directed at a light valve (display panel) all at thesame time with different colors being incident on different areas of thelight valve. This has the advantage of using all of the light energyavailable (all of the red, green or blue light is potentially used allof the time). However, with the separate beams, the required panel sizebecomes quite large. In other words, the etendue (optical extent, whichis the minimum area multiplied by the solid angle) of the illuminationbeam in the light valve illumination system is made bigger. Because ofthis, this type of system uses a very large light valve (larger than 1.1inch diagonal), which increases both the light valve cost and the costsof the associated illumination and projection optics.

[0018] In another system, sequential color recapture (such as set forthin U.S. patent application Ser. Nos. 2002/0,005,914 to Tew,2002/0,135,862 to Dewald, and 2001/0,008,470 to Dewald, the subjectmatter of each being incorporated herein by reference), a light pipe(also referred to as a light tunnel) has a mirrored internal surfacewith an aperture at one end (where light from the light source enters)and a color wheel having spiral bands of color disposed proximate to theother end. When white light passes through the light pipe and isincident on a particular band of the spiral color wheel (e.g. a redband), a color is transmitted (e.g. red light) with the remainder of thelight (e.g. green and blue) being reflected back into the light pipe.Such reflected light is incident on the reflective surface (around theabove mentioned aperture) at the other end of the light pipe and isagain incident on the color wheel, with some of the green light that hadbeen reflected now passing through a green band, some of the blue lightnow passing through a blue band. With multiple instantaneousreflections, much of the light that does not pass through the colorwheel the first time will pass through adjacent bands after beingreflected back into the light pipe. Though more light passes through thecolor wheel in such a system, because the exit of the light pipe issignificantly larger than the entrance (due to the aperture at the lightpipe entrance), the etendue is increased, yet the light recycling isincomplete, offering a compromised advantage.

[0019] Thus there is a need for a system that can recycle color withoutincreasing beam size (and illumination light bundle etendue), andwithout significantly increasing system complexity.

[0020] This invention accomplishes color recycling by recycling lightthat is reflected from a changing color filter, such as a color wheel,drum, cone, or color selective panel (such as a Colorlink device), anddirecting back through the arc.

[0021] A first embodiment of the invention is illustrated in FIG. 1.Illustrated are a light source 1, such as an arc lamp, a first reflector3, a second reflector 5, and a light pipe or tunnel 7. Forward light(light that is emitted by the arc lamp 1 in the direction going to theright in the figure) is reflected by the first reflector 3 back to thesecond reflector 5 via the arc lamp, and on to light pipe 7. Firstreflector 3 can be a spherical reflector as shown, or an elliptical orother reflector. The second reflector 5 can be an elliptical reflectoras shown, or other suitable reflector (including a spherical or otherreflector). Backward light from the light source 1 (light directed fromthe arc lamp to the left in the drawing) is focused first on the secondreflector 2 and then enters light pipe 7. The light that is reflected byreflector 3 back through the arc lamp has been observed to be about 70%efficient because some parts of the arc plasma re-absorb the light.Reflector 3 can be a reflector disposed adjacent the arc lamp, or it canbe a reflective coating coated directly on the side of the lamp.

[0022] After light is reflected from the second reflector 5, it entersthe light pipe 7, passes therethrough and is incident on the colorselective element 10—in this case a color wheel. The color selectiveelement could be one of many types of optical elements that divide whitelight from the light source into individual color bands—either a movingpart (cone, wheel, drum) or some other type of color selective device,for example one based on liquid crystals or MEMS. As mentioned abovewith respect to prior art color wheels, not all light will pass throughthe color selective element—some will be reflected back into the lightpipe. In the present invention, this reflected light is reflected backthrough light pipe 7, is reflected from second reflector 5, throughlight source 1 and is finally incident on first reflector 3. Onceincident on first reflector 3, the light is effectively “recycled” bybeing passed once again though the light source 1, via the secondreflector 5 back into light pipe 7. This “recycled” light is once againincident on the color selective element with more passing through thesecond time (and third and fourth, etc.).

[0023] Light which passes the color selective element 10 is incident onthe light valve 12. Light valve 12 is an array of pixels that areselectively actuated in analog or digital mode to direct light to target14 (e.g. a viewing screen). Light valve 12 can be an array of forexample liquid crystal cells or micromirrors. Also shown in FIG. 1 arecondensing optics 16 (for focusing the light toward the light valve 12,projection optics 17, and TIR (total internal reflection) prisms 18.These optical elements can of course be of various designs (e.g. omitthe TIR prisms 18, multiple lenses for either optics 16 or optics 17,etc.). As will be seen better in FIG. 6, multiple colors from the colorsequencing element are incident on the light valve at the same time butin different areas of the light valve. As such, the filter wheel imageis focused onto the light valve so that there are sharp transitionsbetween colors, and the illumination colors at the valve correspond tothe colors at the color filter element.

[0024] An alternative approach is shown in FIG. 2. As can be seen inthis figure, an additional lens (or group of lenses) 20 is used to imagethe end of the light pipe onto the color wheel/filter. One practicalissue with the color wheel is that it is difficult to get it close tothe end of the light pipe. If it is spaced away from the light pipe,then some light will leak out at the edges. That is, some light whichexit the light pipe at an angle and is located at the very edge of thelight pipe (in FIG. 1) could reflect from the color wheel and notre-enter the light pipe. The extra lens of FIG. 2 allows the image ofthe light pipe exit exactly focus at the color wheel, so less light islost. Also illustrated in FIG. 2 is a third reflector 22 at the lightsource. This third reflector reflects light coming back from light pipe7 that does not pass around the light source toward reflector 5, but isincident on a back side of the light source. This third reflector,whether part of the light source or a separate reflective element, canbe curved or planar and aids in the light recycling and thus overallbrightness of the display.

[0025]FIGS. 3 and 4 are similar to FIGS. 1 and 2, respectively, but areembodiments where the first reflector 3 from FIGS. 1 and 2 is absent.FIG. 5 shows an embodiment in which a spherical lens is used to couplelight to the light pipe. Reflector 5 in this embodiment is a sphericalreflector.

[0026] Etendue (the extent of the beam) is not increased in the approachof this invention. Light that is not selected by a color filter elementis sent back to the arc lamp which is configured so that the light willbe reflected back into the illumination system. In an embodiment of theinvention, any change in etendue is less than 20%; preferably less than10%. This enables the valve size to remain small.

[0027]FIG. 6 shows what one type of color sequencing device—in this casea color wheel with thin “pie wedges” of different colors (e.g. red,green and blue—or red, green, blue and white or another less saturatedlight boost color) that could be placed at the end of the light pipe, acolor wheel, will look like. A color wheel with spiral color bands couldbe used as mentioned above, or another design—though whatever design isselected more than one color (preferably three or more colors) should“overlap” the end of the light pipe at a time so as to take advantage ofthe color recycling (or at least allow more than one color—preferablythree or more colors to be incident on the light valve at any one time).In. FIG. 6, approximately 3 spokes, separating three colors, are shownsuperimposed on the light valve exit.

[0028]FIGS. 7a and 7 b are illustrations of the end of the light pipethat faces towards the light source. FIG. 7a is an illustration of aprior art light pipe that comprises a closed end except for an aperturethrough which a beam of light from the light source enters into thelight pipe. Light pipes with both types of openings facing the lightsource are known—however, till now, the opening of FIG. 7a was used witha color recycling type color sequencer (one that allows for multiplecolors to be incident on a light valve at any one time), whereas theopening of FIG. 7b has been always used with a light valve where, exceptat color transitions, a single color is directed at the light pipe atany one time—and never three colors at any one time. The light pipe ofFIG. 7b is used in the embodiments of the present invention. Though theopening need not be fully open as in FIG. 7b, no more than 50% of thearea of the opening should be covered—preferably no more than 25%, andmore preferably no covering at all, such as illustrated in this figure.By removing the restricted opening at the end of the light pipe, almostall of the light reflected from the color sequencing device back intothe light pipe—passes out of the light pipe back to the light source. Itis preferred that, if the opening is partly restricted, the restrictionis not great—and at least 60% (preferably at least 70%, at least 80% or90% or more) of the light that is reflected off of the color sequencingdevice will pass out of the light pipe to the light source though alower percentage of light can reach the light source (10% or more, 20%or more, or 30% or more), the higher percentages are preferred. Also,the light pipe can have different entrance and exit shapes with apreferably smooth transition between the differently shaped ends of thepipe.

[0029] In the present invention, a highly reflective reflector can bepositioned very close to the arc lamp burner. In one example of theinvention, the light source is a UHP lamp with a reflective coatingdirectly on the lamp. The reflective coating can be a dichroiccoating—preferably one that reflects visible light but transmits lightof other wavelengths. The coating or separate reflector 3 allows for thereflector 5 to focus light inside an angle of 20 degrees or less, oreven 16 degrees or less. The arc length can be 1.3 mm or less, or even1.0 mm or less. If a very short arc length is desired, an around 0.7 mmarc length can be used. A short arc length, combined with the reflector(or reflective coating) that redirects light back through the lamp, andcombined with the color sequencing device as disclosed herein, resultsin a bright light beam incident on the light valve, which, due to thelower etendue of the system, allows for a small light valve thusincreasing the brightness of the projected image. The light valve canhave a diameter of around 0.5 cm or less, or even around 0.4 cm or less,depending upon the optical system components selected.

[0030] There are many variations possible.

[0031] The light pipe or illumination system can be anamorphic.

[0032] This system can be used for either MEMS or LC devices, and ineither transmissive or reflective mode.

[0033] The arc lamp could be rotated so that the arc lamp axis isperpendicular to the illumination optical system axis.

[0034] A parabolic arc lamp reflector could be used.

[0035] An illumination configuration similar to that used in liquidcrystal display projection systems—with two sets of fly's eye lensesand/or polarization conversion being used (not illustrated). In such anembodiment, there is a color selective filter element that is imagedonto the valve, and which reflects unwanted light back into an arc lampwith high retro-reflection capability.

[0036] More than three colors (Red, Green, Blue) could be used toincrease the color gamut (red, green, blue, magenta and yellow, forexample).

[0037] Because the light coming back out the light pipe is spread out,it will more efficiently make its way through and back out of the arc,since it will not focus on the “hot spots”.

[0038] The illumination system does not need to use a TIR prism. Anapproach using a field lens in front of the light valve, or light thatconverges onto the light valve, can also be used. Many known projectionsystem configurations could be used with the present invention.

[0039] The invention disclosed herein is presented in preferredembodiments of projection system design to exemplify the inventivefeatures, but the scope of the invention is much broader thanillustrated with these preferred embodiments. The scope of the inventionis intended to be broadly interpreted to cover the general field ofprojector design.

I claim:
 1. A projection system, comprising: a point source of light anda reflector proximate to the point source of light; a color sequencer,wherein the point source of light, reflector and color sequencer arearranged such that the light from the point source of light is directedso as to be incident on the color sequencer, and wherein at least 10% ofthe light that is reflected back from the color sequencer impinges onthe reflector proximate to the point source of light and is reflectedback so as to again be incident on the color sequencer.
 2. Theprojection system of claim 1, wherein at least 20% of the light that isreflected back from the color sequencer impinges on the reflectorproximate to the point source of light and is reflected back so as toagain be incident on the color sequencer.
 3. The projection system ofclaim 2, wherein at least 30% of the light that is reflected back fromthe color sequencer impinges on the reflector proximate to the pointsource.
 4. The projection system of claim 1, wherein the point source oflight is an arc lamp.
 5. The projection system of claim 4, wherein thereflector is a spherical reflector proximate the arc lamp.
 6. Theprojection system of claim 5, wherein the spherical reflector is areflective coating on the glass bulb of the arc lamp.
 7. The projectionsystem of claim 5, further comprising first optics disposed between thearc lamp and the color sequencer, wherein the first optics is positionedfor focusing light from the arc lamp and reflector proximate to the arclamp onto the color sequencer.
 8. The projection system of claim 7,further comprising a light pipe positioned between the first optics andthe color sequencer.
 9. The projection system of claim 5, furthercomprising a light valve disposed to receive multi colored light fromthe light sequencer.
 10. The projection system of claim 9, wherein thecolor sequencer is capable of forming a spatial and temporal sequence ofcolors that are incident on the light valve.
 11. The projection systemof claim 9, further comprising second optics for focusing light from thecolor sequencer onto the light valve.
 12. The projection system of claim9, further comprising third optics for projection light from the lightvalve onto a target.
 13. The projection system of claim 1, wherein thecolor sequencer is a color wheel, drum, cone or color selective panel.14. The projection system of claim 9, wherein the color sequencer is acolor wheel capable of passing multiple colors onto the light valve atthe same time.
 15. The projection system of claim 1, wherein the lightvalve is a micromirror array.
 16. The projection system of claim 1,further comprising a second reflector facing said reflector and disposedto direct light to the color sequencer.
 17. The projection system ofclaim 16, further comprising a light pipe.
 18. The projection system ofclaim 17, wherein said reflector is a spherical reflector.
 19. Theprojection system of claim 18, wherein the second reflector is anelliptical reflector.
 20. The projection system of claim 16, whereinlight reflected from the color sequencer is incident on both saidreflector and said second reflector so as to be again directed on thecolor sequencer.
 21. A projection system, comprising: an arc lamp; aspherical reflector proximate to the arc lamp; a color sequencer;wherein the arc lamp, spherical reflector and color sequencer arearranged in the projection system such that the light from the arc lampis directed so as to be incident on the color sequencer, and wherein atleast a portion of light that is reflected back from the color sequencerimpinges on the spherical reflector so as to reflected and again beincident on the color sequencer.
 22. The projection system of claim 21,wherein at least 20% of the light that is reflected back from the colorsequencer impinges on the spherical reflector proximate to the arc lampand is reflected back so as to again be incident on the color sequencer.23. The projection system of claim 22, wherein at least 30% of the lightthat is reflected back from the color sequencer impinges on thespherical reflector proximate to the arc lamp.
 24. The projection systemof claim 21, wherein the arc lamp is a UHP burner.
 25. The projectionsystem of claim 24, wherein the spherical reflector is a reflectivelayer on the arc lamp.
 26. The projection system of claim 25, whereinthe spherical reflector is a reflective coating on the glass bulb of thearc lamp.
 27. The projection system of claim 26, further comprisingfirst optics disposed between the arc lamp and the color sequencer,wherein the first optics is positioned for focusing light from the arclamp and spherical reflector proximate to the arc lamp onto the colorsequencer.
 28. The projection system of claim 27, further comprising alight pipe positioned between the first optics and the color sequencer.29. The projection system of claim 25, further comprising a light valvedisposed to receive multi colored light from the light sequencer. 30.The projection system of claim 29, wherein the color sequencer iscapable of forming a spatial and temporal sequence of colors that areincident on the light valve.
 31. The projection system of claim 29,further comprising second optics for focusing light from the colorsequencer onto the light valve.
 32. The projection system of claim 9,further comprising third optics for projection light from the lightvalve onto a target.
 33. The projection system of claim 21, wherein thecolor sequencer is a color wheel, drum, cone or color selective panel.34. The projection system of claim 29, wherein the color sequencer is acolor wheel capable of passing multiple colors onto the light valve atthe same time.
 35. The projection system of claim 21, wherein the lightvalve is a micromirror array.
 36. The projection system of claim 21,further comprising a second reflector facing said spherical reflectorand disposed to direct light to the color sequencer.
 37. The projectionsystem of claim 16, further comprising a light pipe.
 38. The projectionsystem of claim 37, wherein said reflector is a spherical mirror elementdisposed adjacent to the arc lamp.
 39. The projection system of claim38, wherein the second reflector is an elliptical reflector.
 40. Theprojection system of claim 36, wherein light reflected from the colorsequencer is incident on both said spherical reflector and said secondreflector so as to be again directed on the color sequencer.
 41. Aprojection system, comprising: a UHP lamp having a dichroic coating; acolor sequencer; wherein the UHP lamp with dichroic coating and colorsequencer are arranged in the projection system such that the light fromthe UHP lamp is directed so as to be incident on the color sequencer,and wherein at least a portion of light that is reflected back from thecolor sequencer impinges on the dichroic coating so as to reflected andagain be incident on the color sequencer.
 42. The projection system ofclaim 41, wherein at least 10% of the light that is reflected back fromthe color sequencer impinges on the dichroic coating of the UHP lamp andis reflected back so as to again be incident on the color sequencer. 43.The projection system of claim 42, wherein at least 30% of the lightthat is reflected back from the color sequencer impinges on the dichroiccoating of the UHP lamp.
 44. The projection system of claim 41, whereinthe UHP lamp has an arc gap of 1 mm or less.
 45. The projection systemof claim 44, wherein the dichroic coating forms a spherical reflectivesurface.
 46. The projection system of claim 45, wherein the sphericalreflector is a reflective coating on the glass bulb of the UHP lamp. 47.The projection system of claim 46, further comprising first opticsdisposed between the UHP lamp and the color sequencer, wherein the firstoptics is positioned for focusing light from the UHP lamp and sphericalreflector proximate to the UHP lamp onto the color sequencer.
 48. Theprojection system of claim 47, further comprising a light pipepositioned between the first optics and the color sequencer.
 49. Theprojection system of claim 45, further comprising a light valve disposedto receive multi colored light from the light sequencer.
 50. Theprojection system of claim 49, wherein the color sequencer is capable offorming a spatial and temporal sequence of colors that are incident onthe light valve.
 51. The projection system of claim 49, furthercomprising second optics for focusing light from the color sequenceronto the light valve.
 52. The projection system of claim 9, furthercomprising third optics for projection light from the light valve onto atarget.
 53. The projection system of claim 41, wherein the colorsequencer is a color wheel, drum, cone or color selective panel.
 54. Theprojection system of claim 49, wherein the color sequencer is a colorwheel capable of passing multiple colors onto the light valve at thesame time.
 55. The projection system of claim 41, wherein the lightvalve is a micromirror array.
 56. The projection system of claim 41,further comprising a second reflector facing said spherical reflectorand disposed to direct light to the color sequencer.
 57. The projectionsystem of claim 56, further comprising a light pipe.
 58. The projectionsystem of claim 57, wherein said reflector is a spherical mirror elementdisposed adjacent to the UHP lamp.
 59. The projection system of claim58, wherein the second reflector is an elliptical reflector.
 60. Theprojection system of claim 56, wherein light reflected from the colorsequencer is incident on both said spherical reflector and said secondreflector so as to be again directed on the color sequencer.
 61. A lightcollecting system comprising a color filter element; and a concentratedlight source illuminating a color filter element; wherein a substantialportion of light that does not pass through said color filter element isreflected back to said light source, and subsequently is reflected backto said color filter element and then passes through a differentlocation of said color filter element with a 10% or less change in theetendue of the system.
 62. The light collecting system of claim 61,wherein the light source is a high temperature gas plasma.
 63. Anoptical system comprising: a multi spectral light source; a reflector atthe light source for reflecting light from the light source; a colorsequencing device disposed to receive light from the reflector and thatspatially passes some colors and reflects others back to the reflector,wherein at least 60% of the light that is reflected from the colorsequencing device is directed back onto the reflector at the lightsource.
 64. The optical system of claim 63, wherein a light tunnel isprovided between the light source and color sequencing device.
 65. Theoptical system of claim 64, further comprising a second reflectordisposed to reflect light from the light source back through the lightsource and to the color sequencing device via the reflector.
 66. Theoptical system of claim 65, wherein the second reflector lowers theetendue of the optical system.
 67. The optical system of claim 63,wherein the reflector is an elliptical reflector.
 68. The optical systemof claim 65, wherein the second reflector is spherical reflector. 69.The optical system of claim 68, wherein the second reflector is acoating on the light source, the light source being an arc lamp.
 70. Theoptical system of claim 65, wherein the second reflector is anelliptical reflector.
 71. The optical system of claim 63, wherein thelight source is an arc lamp having an arc length of 1 mm or less. 72.The optical system of claim 63, wherein the reflector is a sphericalreflector.
 73. The optical system of claim 65, further comprising athird reflector that reflect light into the light tunnel that exits thelight tunnel but is not directed to said reflector.
 74. The opticalsystem of claim 65, wherein the light tunnel does not have a restrictedopening.
 75. The optical system of claim 65, wherein light is recycledback to the reflector while conserving etendue.
 76. The optical systemof claim 63, further comprising focusing optics for focusing light fromthe color sequencing device on the light valve.
 77. The optical systemof claim 76, further comprising projection optics for projecting animage from the light valve onto a target.
 78. The optical system ofclaim 63, wherein at least 70% of the light that is reflected from thecolor sequencing device is directed back onto the reflector at the lightsource.
 79. The optical system of claim 78, wherein at least 80% of thelight that is reflected from the color sequencing device is directedback onto the reflector at the light source.
 80. A projection system,comprising: a light source and a reflector proximate to the lightsource; a color sequencer, wherein the light source, reflector and colorsequencer are arranged such that the light from the light source isdirected so as to be incident on the color sequencer, and wherein atleast 10% of the light that is reflected back from the color sequenceris recycled via the light source by being incident on the reflectorproximate to the light source and is reflected back so as to again beincident on the color sequencer, and wherein the etendue of theprojection system is less than 20% different from a system without lightbeing recycled via the light source.
 81. The projection system of claim80, wherein the etendue is less than 10% different from a system withoutlight being recycled via the light source.
 82. A projection system,comprising: a light source and a reflector proximate to the lightsource; a spatial light modulator; a color sequencer that provides threeor more different colors onto the spatial light modulator at the sametime; wherein the light source, reflector and color sequencer arearranged such that the light from the light source is directed so as tobe incident on the color sequencer, and wherein at least 60% of thelight that is reflected back from the color sequencer to be incident onthe reflector proximate to the light source and is reflected back so asto again be incident on the color sequencer.
 83. The projection systemof claim 82, wherein at least 70% of the light that is reflected backfrom the color sequencer to be incident on the reflector proximate tothe light source and is reflected back so as to again be incident on thecolor sequencer.
 84. The projection system of claim 83, wherein at least80% of the light that is reflected back from the color sequencer to beincident on the reflector proximate to the light source and is reflectedback so as to again be incident on the color sequencer
 85. A projectionsystem, comprising: a light source and a reflector proximate to thelight source; a spatial light modulator; a color sequencer that providesthree or more different colors onto the spatial light modulator at thesame time; wherein the light source, reflector and color sequencer arearranged such that the light from the light source is directed so as tobe incident on the color sequencer and has a first etendue, and whereinlight reflected back from the color sequencer is incident on thereflector proximate to the light source and is reflected back so as toagain be incident on the color sequencer with a second etendue less than20% different from the first etendue.
 86. The projection system of claim85, wherein the second etendue less than 10% different from the firstetendue.